Filebeats and xpack modules - Confusion about licensing

In case I'd just like to leverage Filebeats including x-pack modules (such as Office365) and Logstash as part of a backend infrastructure - Is a license needed?

The ingestion process (and Filebeats\Logstash inside) isn't the main value that customers get from the product we provide. We want to incorporate these components just for achieving simpler code. However, seems that x-pack is subject to Elastic License.

The software piece is NOT distributed to the customer directly, but just part of the backend infrastructure (SaaS) and intended to be integrated within the production environment.

Can we make use of it? Any license is required? Is it free of charge? Is it considered as internal-use? I'd like to get clarifications.

You'd be best off emailing elastic_license@elastic.co for the best answers on those.